Cathodic sputtering is widely used for depositing thin layers or films of materials from sputter targets onto substrates. Basically, a cathode assembly including the sputter target is placed together with an anode in a chamber filled with an inert gas, preferably argon. A substrate is positioned in the chamber near the anode with a receiving surface oriented normal to a path between the cathode assembly and the anode. A high voltage electric field is applied across the cathode assembly and the anode causing electrons to eject from the cathode assembly and ionize the inert gas. The positively charged ions of the inert gas are then propelled against a sputtering surface of the sputter target due to the electric field. The ion bombardment against the sputtering surface of the target causes portions of the material of the sputtering surface to dislodge from the sputter target surface and deposit as a thin film or layer on the receiving surface of the substrate at an opposite end of the chamber.
Sputtering targets are typically formed as a generally circular disk of target material, such as aluminum, gold, silver, tantalum, copper, titanium, tungsten or platinum and alloys thereof. The disk of target material may be soldered or otherwise bonded to a supporting target backplate to form a replaceable sputtering target assembly. During the sputtering operation, material is sputtered from the top surface of the target and deposited on the wafer. The sputtering material typically erodes unevenly across the width or face of the target exposed to the wafer, with some areas of the target eroding more quickly than other areas.
Recently, non-planar sputter targets have been developed to provide improved sputtering and deposition uniformity. For example, open-ended cup-shaped hollow cathode magnetron (HCM) sputter targets have been developed, as disclosed in U.S. Pat. No. 6,419,806 of common assignment herewith, the disclosure of which is incorporated herein by reference. These cup or dome shaped targets are generally comprised of a high purity metallic material as the target surface and they are typically formed from well-known metal-working operations such as hydroforming. The closed end of the cup-shaped target comprises a dome. Sidewalls extend from the dome to an open end of the target.
Typically, these cup or dome shaped targets experience the most target material consumption (i.e., erosion) in the dome area with the corner areas that connect the dome to the sidewalls also experiencing considerable erosion but less than that in the dome area. The sidewall areas of the cup shaped target usually experience the least amount of target erosion.